On December 8, 2008, Google announced a new offering from its experimental Labs playground called
Tasks.
Tasks is a to-do list that you can leave open in Gmail so you always have a place to jot
things down (you can finally stop storing things in Gmail drafts!).
Unlike most Web 2.0 to-do lists, Tasks behaves like a notepad,
making it possible to just type instead of having to click all over the place to add or edit your to-dos.

A Google Apps user whose domain is example.com can get to the mobile version of Tasks at
mail.google.com/tasks/a/example.com/.

The appropriate link to Tasks should also be available from the mobile version of Gmail
(assuming the Tasks lab is already enabled for your Gmail account).
However, it is better to create a separate bookmark to Tasks in the
unfortunate event that Gmail is unavailable.

If you are a Google Apps user and
you get a strange error when you visit Tasks on your phone, contact an administrator for your domain and make sure he or she has enabled the
Turn on new features setting, as explained in this
help center article.
Note: It may take some time for Apps to reflect the new setting for your domain.

Some users noted that the XHTML view mentioned in the previous tip
(http://mail.google.com/tasks/m)
also works well as a printable version of Tasks from a web browser.
If you really need to print, give it a shot!

If you have an understanding of iGoogle gadgets,
you may have figured out that the Tasks gadget is simply a pointer to
http://mail.google.com/tasks/ig,
which can be opened in its own page in your browser,
giving you a full-screen view of Tasks.
As explained on LifeHacker,
this page also works well as a sidebar in Firefox so your tasks are always visible,
even when you're not in Gmail.

iGoogle users who have the Tasks gadget installed can use the Maximize button in
the upper-right-hand corner of the gadget so it expands to fill the iGoogle page.

The solution for this one is really simple: put the most important things at the top of the list.
Mouse down on a task's checkbox (or the "grippy" to its left) to "pick up" a task and drag it
anywhere on the list. Watch as lesser important tasks move out of the way as you reprioritize your list!

Keyboard users can also use control-up/down (⌘-up/down on a Mac) to move a task through the list.

On the bottom of the "details" page for a task, there is a Move to list dropdown
that lets you choose which list you would like to move the task to.
You can access the details page by any of the following methods:

Clicking on the arrow that appears on the far right when you mouse over a task.

Pressing shift+enter when a task has keyboard focus.

Choosing Edit details from the Actions menu when a task is selected.

From the details page, you can also add notes to a task or assign it a due date.

Many of the blog posts about Tasks have touted the feature that lets you add an
email as a task. This is not limited to messages in your inbox!
For example, if you want to create a task to make sure someone responds to
an email you have sent, select the email in Sent Mail and use
More actions -> Add to Tasks, just like you would with any other message.
Similarly, if you have a task that is based around a chat conversation,
you can go to Chats, find the conversation, and create a task from that in the same way.

Unfortunately, sometimes Gmail goes down. When that happens, the whole Web is a-twitter
(pun intended), but that doesn't mean that Tasks is unavailable! If you already have the
iGoogle gadget installed, you will still be able to check Tasks from iGoogle.
Similarly, if you have Tasks bookmarked on your mobile phone, you can get to it
from there, too.

Don't have Tasks in Gmail yet?

Well what are you waiting for?
You can follow these instructions
to enable Tasks in Gmail. (Sorry, I couldn't find instructions that included screenshots.)